Various forms of atomisers are known and have been used for applying liquids to plant foliage or areas near the plants. As an example agricultural chemicals such as pesticides or weedicides are applied by this technique to protect economic plants from insects and weeds. Droplet size of the liquid after atomisation is important in determining the efficiency by which the liquid is deposited on the target. If the droplets are less than optimum size the efficiency of deposition on the target can be reduced by factors such as wind. Similarly if the droplets are larger than optimum sufficient numbers of droplets may not be produced for adequate target coverage, they may run off the target without sticking, or they may fall to the ground under the influence of gravity before reaching the target.